In recent years, attention is being given to an organic EL display utilizing organic EL (Electro Luminescence) as one of next generation flat-panel displays that replace liquid crystal displays.
An organic EL display includes an organic EL panel in which a plurality of display pixels are disposed in a matrix form. Each display pixel has an organic EL element and a drive transistor that supplies a drive current according to a pixel signal to the organic EL element.
In an active matrix type display device such as an organic EL display, a thin film transistor (TFT) is used as a drive transistor. In a TFT, a threshold value voltage of the TFT shifts over time due to stress such as a voltage between the gate and source when energized. The shift of a threshold value voltage over time causes a variation in the amount of current supplied to the organic EL, and thus has an effect on brightness control of the display device, and the display quality is reduced.
In addition, in an organic EL element, due to stress of a current that flows through the organic EL element, the brightness decreases over time even with the same amount of current supplied. The decrease in the brightness over time causes the display quality to deteriorate.
In an organic EL display, in order to prevent deterioration of the display quality, a cumulative value of stress (hereinafter briefly called a “cumulative value” as needed) for each of the organic EL element and the TFT is determined, and the gradation values in a video signal are corrected using the cumulative value.